The invention relates to an advanced formulation scale conditioning process and composition for enhancing the removal of films, scales, and sludge deposits from industrial process vessels, such as shell and tube heat exchangers, boilers, and steam generators.
Metal surfaces exposed to water or aqueous solutions over long periods of time in closed heat transfer systems develop scales and/or become covered by sludge and other deposits, regardless of the system water purity levels. For example, in commercial electric power generating plants, after on-line operation at temperatures of 200° C. or more, large shell and tube heat exchangers, such as those known as nuclear steam generators, develop adherent scales and/or sludge deposits on the secondary side surfaces of tubes, tube sheets, tube support plates, and other internal structural parts. These troublesome scales and deposits form even in those instances in which the purity of the water may be controlled to levels at or below parts per million. Over a period of time, the accumulation of these scales and sludge will have an adverse effect on the operational performance of the steam generators.
Various off-line cleaning methods have been developed to remove the scales and sludge built up on the internal surfaces of heat exchangers used to generate steam. Commercially successful methods include: pressure pulsing with shock waves; water slapping; chemical cleaning at elevated temperatures, using a variety of chelants at concentrations ranging between approximately 5 and 25%; use of scale conditioning agents at elevated pH (around 10.5); and flushing with high pressure water. Both pressure pulse and chemical methods for cleaning the interior of heat exchanger vessels such as the secondary sides of nuclear steam generators are known in the prior art. U.S. Pat. No. 4,899,697 (Franklin, et al.), U.S. Pat. No. 4,921,662 (Franklin, et al.), U.S. Pat. No. 5,006,304 Franklin, et al.), U.S. Pat. No. 5,092,280 (Franklin, et al.), and U.S. Pat. No. 5,092,355 (Cadwell, et al.) all disclose pressure pulse cleaning methods and devices to loosen and remove sludge and debris from heat exchanger surfaces within the secondary side of nuclear steam generators by means of shock waves introduced in water. U.S. Pat. No. 5,019,329 (Franklin, et al.) discloses an improved cleaning method for the secondary side of nuclear steam generators by means of vertically flushing the secondary side of nuclear steam generators during pressure pulse or other shock wave type cleaning operations.
The scale conditioning agent formulations disclosed in U.S. Pat. No. 5,764,717 to Rootham and U.S. Pat. No. 5,841,826 to Rootham et al. were designed to minimize interaction with magnetite, the principal component of most scale and hardened sludge deposits. The advanced formulation scale conditioning agents of the present invention, however, have the ability both to interact with magnetite causing controlled dissolution and to assist in removing copper and silicate enriched hydrothermal minerals. Highly densified magnetite generally resists penetration by prior art scale conditioning agents comprising combinations of strongly basic amines and intercalation agents. The improved scale conditioning agents of the present invention, however, by overcoming overcoming these limitations, are especially useful in removing scales and other deposits which are composed principally of homogenous and highly densified magnetite.